MICROBIOLOGY OF AIR by DR.E.OLOTON.docx

**PMB 313: Disinfection and Sterilization (2021)** **Microbiology of air** Brief history of air microbiology A. Discovery of microorganism 1. 1676: A. Leeuwenhoek -- first to observe and describe microbes accurately 2. 1884: C. Chamberland -- constructed a bacterial filter that allowed...

**PMB 313: Disinfection and Sterilization (2021)** **Microbiology of air** Brief history of air microbiology A. Discovery of microorganism 1. 1676: A. Leeuwenhoek -- first to observe and describe microbes accurately 2. 1884: C. Chamberland -- constructed a bacterial filter that allowed the identification of viruses **FACTORS INFLUENCING THE BIOAEROSOLS** **MICROBIOLOGICAL ASSESSMENT OF HOSPITAL AND PHARMACEUTICAL INDUSTRIES** Assessment of the hospital and pharmaceutical industries can be determined using air samplers.The two air sampler techniques are: active air samplers or by passive air sampling. [Passive air sampling]: Sedimentation sampling Sedimentation sampling is a static method that relies on the force of gravity and air currents to cause the settling of airborne microorganisms onto agar plates filled with general and selective media. Standard 90 mm diameter plates are placed throughout the processing facility for about 15 minutes to 1 hour. After exposure the plates are incubated for an appropriate time and temperature. Sedimentation results are expressed as CFU (colony forming units) or particles per minute of exposure. This technique is inexpensive, easy, and collects bioaerosols in their original state. The main disadvantage of this method is its inability to measure the number of viable particles per volume of air. Other disadvantages of this method are long sampling times, great reliance on air currents, bias towards large particles and low correlation with counts obtained using other methods. [Active air sampling ] The microbial air contamination can be measured by counting the number of cfu per cubic metre (cfu/m^3^ ) of air. Active air samplers are used, which collect a known volume of air, blown on to a medium by different techniques which involve the control of air current. Impaction method: The majority of air samplers used in the pharmaceutical industry use impaction as the method for collecting bioaerosols. Impaction methods use the inertia of particles to separate them from the air currents. Impactors collect airborne microorganisms onto an agar surface or an adhesive coated surface with the use of a vacuum. An impactor consists of an air jet that is directed over the impaction surface causing the particle to collide and stick to the surface. There are two types of impactors: slit (i.e. STA, New Brunswick Sci. Co. Inc., Casella, BGI Inc.) or sieve (i.e. Andersen sampler, Thermo Electron Corp.) samplers. A slit sampler is cylindrical in shape and has a tapered slit tube that creates a jet stream when an air samples is pulled by a vacuum. The air sample is collected onto an agar plate which is rotating on a turn table to create an even distribution of particles. A slit sampler requires a vacuum to draw a constant flow rate of usually 28.3 liters per minute. Sieve samplers function by drawing air (i.e. 28.3 l/min) through a metal plate with many small holes. Air particles impact on the agar surface which is a few millimeters below the metal sieve. Sieve samplers like the Andersen sampler may consist of a single stage or two, six or eight stages. The stages of a multiple stage sampler have decreasingly smaller holes causing increased particle velocity as the air travels through the sampler. Large particles are impacted on the first stages and smaller particles are carried until they are accelerated enough to impact the later stages. Multiple stage impactors are not only used for the enumeration of viable particles per unit volume of air, but also yield a size profile of particles in the bioaerosol. A two stage impactor is used when the differentiation between respirable particles (5 µm) is of interest. Multiple stage impactors are used more in health care settings. Single stage impactors do not differentiate between particle sizes and are used when the total number of viable particles per unit volume of air is needed. Impaction methods obtain higher recovery rates than other air sampling methods and are used when bioaerosol levels are expected to be low. This method results in a low sampling stress and after collection no further manipulation is needed because particles are on agar plates. Impactors possess relatively high sampling efficiencies, are rugged and simple to operate. Some disadvantages of this method are that these samplers are usually difficult and bulky to handle, expensive, and cumbersome. Also the inside of the sampler and the outside of the agar plates must remain sterile until sampling begins or else samples may become contaminated. [Filtration method:] The filtration method collects airborne microorganisms onto a filter which is mounted on a holder and connected to a vacuum source with a flow rate controller. The filter can consist of sodium alginate, cellulose fiber, glass fiber, gelatin membrane (pore size 3 µm) or a synthetic membrane (pore size 0.45 µm or 0.22 µm). Gelatin membrane filters are water-soluble and can be placed directly onto an agar surface for quantification or can be serially diluted in a liquid first. Synthetic membrane filters are agitated in a liquid to disperse the particles before bacteriological analysis is performed. Filter collection devices are used for the enumeration of molds or bacterial spores but are less effective for vegetative cells because of the stress associated with desiccation, although shorter sampling times could reduce this stress. Filtration devices are low in cost and simple to operate and their filters possess a large number of pores so that large volumes of air can be sampled during a short period of time. [Impingement method]: Impingement methods use a liquid medium for the collection of airborne microorganisms. Air particles are entrapped in the liquid as air is dispersed through the liquid. Liquid impingersare either low velocity or high velocity. Low velocity impingers do not efficiently collect small particles (\